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Abstract

Background

To confirm or refute the hypothesis that the morbidity of children (since birth to
age 5) born and living in the heavily polluted (PM10, benzo[a]pyrene) eastern part of Ostrava, Czech Republic, was higher than the morbidity
of children living in other parts of the city.

Methods

Ten pediatricians in 5 districts of Ostrava abstracted the medical records of 1878
children born in 2001–2004 to list all illnesses of each child in ICD-10 codes. The
children were divided into four groups according to their residence at birth and thereafter.
Most of the children in the eastern area were living in the city district Radvanice
and Bartovice.

Results

We report on the incidence of acute illnesses in 1535 children of Czech ethnicity
in the first 5 years of life. The most frequent acute illnesses (over 45% of all diagnoses)
were upper respiratory infections (URI: J00-J02, J06). In the first year of life,
the incidence of URI in 183 children in the eastern area – 372 illnesses/100 children/year
– was more than twice as high as in the other 3 areas with a total number of 1352
children. From birth to the age of 5 years, the incidences of pneumonia, tonsillitis,
viral infections (ICD-10 code B34) and intestinal infectious diseases were also several
times higher in children living in the eastern part of Ostrava. The lowest morbidity
was found in children living in the less polluted western part of the city.

Conclusions

The children born and living in the eastern part of the city of Ostrava had from birth
through 5 years significantly higher incidence rates of acute illnesses than children
in other parts of Ostrava. They also had a higher prevalence of wheezing, atopic dermatitis
and allergic rhinitis.

Keywords:

Background

The city of Ostrava is the largest industrial city in the Moravian-Silesian region
(MSR) of the Czech Republic. This region is bordered on the west, east and partially
also on the south by mountains, forming a basin with frequent winter temperature inversions.
The region is a heavily polluted industrial area. Concentrations of PM10, PM2.5, and benzo[a]pyrene (B[a]P) significantly exceed limit values [1]. The most important industrial sources of air pollution are metallurgy, steel plants,
coke ovens and power generating facilities [2]. The population density in the MSR is also associated with high-intensity local vehicular
transport and local heating. Almost fifty percent of the MSR inhabitants use central
heating, 34% natural gas, 10% coal, 3% electricity, and 3% wood [3]. The prevailing wind direction in Ostrava is SW (especially in winter), with NE winds
being the second most frequent. The episodes of highest immissions depend on the wind
direction and speed, locality and season [4]. A contribution of sources located on Polish territory to the air pollution load
in the city of Ostrava cannot be excluded [5]. Among the extremely polluted areas is the Ostrava city district Radvanice and Bartovice
(R&B, Figure 1). One part of the research project Airgen aimed at analyzing the morbidity of children
in Ostrava to confirm the hypothesis that children living in a polluted environment
in R&B suffer more frequently from acute respiratory infections than children living
in cleaner parts of Ostrava. We have compared the incidence rates of respiratory infections
and other acute illnesses as well as the prevalence of allergic diseases in preschool
children registered at 10 pediatric offices in 5 districts of the city of Ostrava.

Methods

Ostrava study

In 2009 and 2010 a total of 1887 children born in 2001–2004 and registered with 10
pediatric offices in 5 districts of the city of Ostrava took part in the study. An
informed consent signed by the parents was approved by the Ethical Committee of the
Institute of Experimental Medicine of the Czech Academy of Sciences. Mothers were
asked to complete a written questionnaire on the home environment of the child, including
indoor air pollution sources and other factors potentially related to respiratory
illnesses, i.e., breastfeeding, day-care, the number of older siblings, the number
of smokers in the household, the type of flat, heating of the flat, family history
of allergies, keeping pets, mold and dampness in flat etc. We have also asked mothers
to give pediatricians an informed parental permission to inform us about the present
health status of children and all illnesses they suffeered from birth to the age of
6. We have not done any further follow-up or collected any biological samples.

The pediatric questionnaire included information about delivery, breastfeeding, congenital
defects, serious chronic illnesses, allergies and the results of skin testing. The
pediatricians abstracted their medical documentation to list in the codes of International
Classification of Diseases, Tenth Revision (ICD-10) all illnesses of the child from
birth to the age of 6 years. For the purpose of analysis, the diagnoses were integrated
into broader groups (Table 1).

Table 1.The major disease groups in children of Czech ethnicity from birth to age of 5

Geographical stratification according to the levels of ambient pollution

In 1997 Williams et al. [6] followed the exposure of adults to benzo[a]pyrene in Ostrava using both personal
and stationary monitors. To this end they divided Ostrava into three regions according
to previous studies that mapped pollution by organics. The first region consisted
of the western part of the city, while the eastern part was divided horizontally (approximately
in the middle) into northeastern and southeastern regions. Because of high levels
of PM10 and benzo[a]pyrene monitored in recent years in the eastern part of the city of Ostrava,
we have further divided the northeastern region and thus we distinguish four Ostrava
regions: west, center, east and south (Figure 1). The yearly means of PM10 for each locality of residence were calculated using GIS and the data from surrounding
monitoring stations in Ostrava, also taking into consideration the prevailing wind
direction. The concentrations of PM10 were determined by two-dimensional interpolation of data from the nearest monitoring
stations. The total means of PM10 for the four Ostrava regions were weighted by the number of children taking part
in our study in each locality (Table 2). The yearly means of B[a]P are values measured by stationary monitoring stations
in O. east, west and center. There are no data for O. south (Table 2).

Table 2.Weighted yearly means of PM10 and the yearly means of benzo[a]pyrene

Children

In the Czech Republic each child has to be registered with a pediatrician. In 8 out
of 10 participating pediatric offices, more than 90% of registered children (1583
children) took part in the study. In the remaining two offices 69.7% and 74.1% of
registered children participated (304 children). In total 1887 children took part
in the study. Subsequently applied exclusion criteria included being born outside
Ostrava (92 children), birth weight <1500 grams (54 children), congenital defects,
tumors, cerebral palsy and long-term preventive administration of antibiotics (27
children), incomplete medical documentation (5 children) and a stay in a children’s
home (1 child). The present report is focused on children of Czech ethnicity since
their lifestyle and proneness to allergies differ from those of Roma children [7]. The analysis of morbidity was also limited to children born in at least the 36th
week of gestation and still living in the same region of Ostrava where they were born.
The follow-up of children who spent in the current year less than 11 month at the
original address (i.e., region of Ostrava) was discontinued. Therefore, the number
of children in the present study decreased from 1535 in the first year of life to
1404 in the 5th year (Table 3). We do not report on the morbidity of children in the 6th year of life because we
do not have the data for children born in 2004. The diagnoses of particular illnesses
in ICD-10 codes were merged into broader groups (Table 1). The group of upper respiratory infections (URI) included codes for the diagnoses
acute nasopharyngitis (common cold, J00), acute pharyngitis (J02) and acute upper
respiratory infections of multiple and unspecified sites (J06).

Table 3.Numbers of children included in the present analysis stratified according to their
residence and age

Statistics

The Kruskal-Wallis equality-of-populations rank test was used for bivariate analyses.
Given that the frequencies of most illnesses in individual children were extremely
variable, negative binomial regression, suitable for overspread variables, was used
for multivariate analyses of the associations of the regions of residence with the
incidence rates of respiratory illnesses. The significance of associations was determined
by the rate ratio (RR), statistically significant probability and a 95% confidence
interval not including the value 1. Confounders were determined by changes in the
regression coefficient of more than 15% after removal of the variable. All tests were
performed using STATA 12 software.

Results

Ambient air pollution

The yearly means of PM10 show that the children born and living in the region O. west were exposed to the
lowest immissions of PM10 (Table 2) as only in 2003 did the yearly mean exceed 40.1 μg/m3. In 2001–2003 there was practically no difference between the rather steep increases
in the yearly means of PM10 in the other three regions of Ostrava. After a decrease in 2004 the PM10 levels started to increase again and peaked in 2006 and 2007. In this period the
levels of PM10 in the four Ostrava regions noticeably differed, and the levels of PM10 increased in the order O. west, south, center and east. In the latter region the
mean concentration of PM10 in 2006 reached 61 μg/m3. The yearly means of benzo[a]pyrene are available for the period from 2003 to 2011.
The lowest yearly means in the range 2.1 to 3.7 ng/m3 of B[a]P were observed in O. west. The highest levels in the range 7.9 to 11.7 ng/m3 of B[a]P were recorded by the monitoring station in R&B in the region O. east. From
2003 to 2006 the yearly means of B[a]P in O. east increased by 48%. The 6 months means
of the winter and autumn months ranged from 12.2 to 18.7 ng/m3 in O. east (data not shown). B[a]P was not monitored in O. south.

Age- and region-specific morbidity of children

Acute URI represented 47.4% of the total number of 27,368 diagnoses of acute illnesses
evaluated in our study (Table 1). Their age-specific incidence rates/100 children/year in the four Ostrava regions
are shown in Figure 2. The highest incidence - 372 episodes per 100 children in the first year of life
- was found in the children from the region O. east. In the second year of life the
incidence rate of URI in O. east decreased by about 50% to the level of the incidence
of URI in O. south, and this similarity persisted to the 5th year of life. The incidence
rates of URI in children living in O. center and O. west were remarkably lower. The
incidence rate of tonsillitis in the 1st year of life of children born and living
in O. east (86/100 children/year) was approximately 8 times higher than in the other
regions of Ostrava. It remained at the same level till the 5th year of life (Figure 3). The incidence rate of tonsillitis in the other regions of Ostrava increased with
age to a maximum of 37/100 children in the 5th year of life in O. south. The incidence
rate of intestinal infectious diseases was highest in the O. east children with a
rate of 81/100 children/year in the 1st year, decreasing to 27/100 children/year in
the 3rd year (Figure 4). The incidence rates in the other 3 regions remained in the range from 6 to 35/100
children/year; the incidence plots for O. center and O. west were almost identical.

Figure 2.Incidence of upper respiratory infections (URI) per 100 children per year of life. Numbers of children stratified by age and region of residence are presented in Table 3.

Figure 3.Incidence of tonsillitis per 100 children per year of life. Numbers of children stratified by age and region of residence are presented in Table 3.

Figure 4.Incidence of intestinal infectious diseases per 100 children per year of life. Numbers of children stratified by age and region of residence are presented in Table 3.

The children in O. east also had the highest incidence rate of viral illnesses, namely
of unspecified viral infections (ICD code B34). The rate of 86/100 children/year in
the 1st year decreased rather slowly to 63/100 children in the 4th year (Figure 5). The incidence rates in children in the other three regions were similar, ranging
from 12 to 24/100 children/year.

Figure 5.Incidence of viral illnesses per 100 children per year of life. The vast majority of diagnoses in O. east were infections of unspecified site (ICD
code B34). Numbers of children stratified by age and region of residence are presented
in Table 3.

Finally, the incidence rate of pneumonia was higher in children born and living in
O. east than in the other regions. It decreased from 17/100 in the 1st year to 8/100
in the 3rd year and remained approximately at this level in the 4th and 5th year (Figure 6). In O. west there was only 1 case of pneumonia in the 1st and another one in the
5th year.

Figure 6.Incidence of pneumonia per 100 children per year of life. Numbers of children stratified by age and region of residence are presented in Table 3. In O. west there was only 1 case of pneumonia in the 1st and another one in the
5th year.

The incidence of otitis media was quite low in the first three years, then peaked
in the 4th year of life in O. south at 24/100 children/year. The peak incidence was
also reached in the 4th year in O. west and east and in the 5th year in O. center.
The plots of the age incidence of laryngitis and tracheitis show two distinctly different
pairings. Children in O. west and O. east had a lower incidence with a plateau from
the 3rd to the 5th year of age (about 15 diagnoses/100 children/year). The other two
plots (O. south and O. center) had their highest values at about 35 diagnoses/100
children/year in the 4th and 5th year of age. The incidence plots of bronchitis peak
in the 4th or the 5th year of age. The highest yearly incidence from the 2nd to the
4th year was found in children living in O. center.

Covariates

Sociodemographics, the indoor environment and other characteristics stratified by
region of residence are presented in Table 4. There were several differences between families living in O. east and in the other
three regions. More mothers in O. east attained the lowest level of education and
fewer mothers attained the highest levels. More mothers smoked during pregnancy and
fewer children were breastfed and attended day care. The biggest differences were
in the type of housing, since in R&B (where most children in our sample from O. east
lived) family houses prevail over apartment block flats and, consequently, space heating
(gas, coal/wood) and mold in flats were more frequent and gas appliances in flats
were less frequent. Also, more children had siblings under 14 with allergies. However,
none of these covariates confounded associations of the increased incidence of acute
infections in children born and living in the O. east region.

Incidence rate ratios

Differences between the incidence rates of illnesses in children living in the four
regions of Ostrava were evaluated in two age categories: from birth to the age of
2 years and from the age of 2 to 5 years (Table 5). Associations of the incidence rates of illnesses with four level region variables
were tested using negative binomial regression. As the basic level we chose residence
in O. east (Table 6). In both age categories the incidence rates of bronchitis and otitis media did not
differ, while the rates of tonsillitis, viral illnesses, and intestinal infections
in the regions O. south, west and center were significantly lower than in O. east.
The rate ratios ranged from 0.51 to 0.11. The incidence rates of URI were significantly
higher than in the remaining regions in the age category of 0–2 years, whereas in
the category 2–5 years there was no difference between the O. east and O. south. The
incidence of pneumonia was significantly higher in the age category 0–2 years and
too low to be tested in the older group. The incidence of laryngitis and tracheitis
in O. east varied with age; in the older category it was lower in O. east than in
O. south and O. center. The RRs were adjusted for gender, type of delivery, neonatal
icterus treated with phototherapy, year of birth, breastfeeding, maternal age and
education, atopic dermatitis, smoking of the mother, exposure to environmental tobacco
smoke, having an older sibling, allergy of an older sibling, type of flat (1st year),
households with a gas appliance and mold in the flat in the 1st year of life. The
multivariate regressions for the age category 2–5 years were also adjusted for recurrent
wheezing, allergic rhinitis and attending day-care in the 4th and the 5th year of
life.

Table 5.Cumulative incidence rates of selected illnesses per 100 children of Czech ethnicity

Prevalence of allergies

The prevalence of allergies was evaluated in 1404 children of Czech ethnicity, born
and living in the city of Ostrava till the age of 5 years, as children of Roma ethnicity
have allergies rather seldom [7]. The overall prevalence of recurrent wheezing (WH) was 14.0%, and the prevalence
of allergic rhinitis (AR) and atopic eczema (AE) were 10.8% and 17.8%, respectively.
The allergies were diagnosed by pediatricians and confirmed by allergists. Only 7
children with reported recurrent wheezing did not see an allergist. The prevalence
of all three diagnoses was the highest in children born and living in the region O.
east: WH 37%, AE 35% and AR 24%. Also, combinations of two or three types of allergy
were most frequent in O. east: 37% of children with WH had also AE, while 57% of children
with WH were also diagnosed with AR. Finally, 43% of children with WH were diagnosed
with all three allergies (Table 7). Skin tests to aeroallergens were applied to most children with a suspected allergy.
The highest percentages of children in all four regions of Ostrava were sensitised
to pollen and mites. The children living in O. east were sensitised less frequently
than children in the other parts of Ostrava (Table 7). However, the panels of tests applied were not necessarily identical.

Table 7.Prevalence of wheezing and allergies among children of Czech ethnicity stratified
by region of residence

Discussion

The primary aim of the study was to prove or refute the hypothesis that infants, toddlers
and preschool children living in the Ostrava district R&B had higher morbidity rates
than children living in other parts of Ostrava. In the Czech Republic, each child
has to be registered with a pediatrician. Due to the high percentage of participating
children registered with 10 pediatricians, our cohort can be considered a representative
sample. We have compared the morbidity of the children by quantifying the incidence
rates of acute illnesses in the first five years of life. Our results unequivocally
prove the high morbidity of children born and living in the region O. east, most of
them in the district R&B. These children had a significantly higher incidence of URI
than children in O. center and O. west (in all years) and in O. south in the 1st year.
Moreover, in all 5 years they had the highest incidence rates of pneumonia, tonsillitis,
intestinal infectious diseases and unspecified viral illnesses. They also had the
highest prevalence of recurrent wheezing, atopic dermatitis and allergic rhinitis
at the age of 5 years. The lowest incidence of most illnesses was seen in children
living in O. west. The children in O. east suffered less frequently from laryngitis
and tracheitis and bronchitis than children in the other regions of Ostrava. The low
incidence of tracheitis and laryngitis in O. east may be explained by the fact that
the environment in O. east is much less urban than in O. south and center. An apparent
reason for the low incidence of acute bronchitis is the high prevalence of recurrent
wheezing (i.e., obstructive bronchitis) and its treatment.

Our previous study on the health of children (birth to age 10) living in the industrial
district of Teplice, Czech Republic [8,9], showed that the incidences of all respiratory illnesses were at the levels seen
in O. west, center or south. The only exception was the high incidence of laryngitis
and tracheitis in children living in the town of Teplice. This is apparently associated
with the urban environment, since the incidence of laryngitis and tracheitis in children
living in the other parts of the district of Teplice was lower. The early onset of
otitis media is considered as typical in many published reports [10,11]. We saw the peak incidence in the 1st and the 2nd year in children living in the
district of Teplice. The highest incidence of OM in Ostrava children occurred in the
4th (O. south, east and west) or the 5th year of life (O. center) [12].

In contrast to the Teplice study, the children in Ostrava were seldom diagnosed with
influenza.

The four regions of Ostrava differ in the levels of pollution by PAHs and PM10. The WHO scientific review [13] stated that in addition to the carcinogenic effects of PAHs (c-PAHs, carcinogenic
polycyclic aromatic hydrocarbons), there is new evidence for early biological effects
of PAHs exposure in both children and adults, and that there are no reasons for changing
the limit value of B[a]P at 1 ng/m3. Miller et al. [14] used personal air monitors for 48 h to determine c-PAHs exposure levels (the sum
of eight PAHs including B[a]P) of women in the 3rd trimester of pregnancy. Their children
at the age 12 months exhibited more frequent coughing and wheezing when their mothers
were exposed to c-PAHs during pregnancy and the children were exposed in the postnatal
period to environmental tobacco smoke. An association of acute respiratory infections,
sore throat and ear infections in the first year of life of children of mothers exposed
to c-PAHs in the second trimester was also suggested by the results of a study performed
in Krakow, Poland, which is a region bordering MSR and similar in its industrial status
and ambient air pollution [15]. The authors explained this observation by the immunotoxic activity of c-PAHs, which
impairs fetal development of the immune system and is responsible for the increased
susceptibility of newborns and preschool children to respiratory infections. Children
living in the region O. south had the second highest incidence rate of URI in the
first year and a slightly higher incidence of URI than the children in O. east in
the age 2–5. PAHs are not monitored in O. south.

Dejmek et al. [16] observed the effect of increasing concentrations of c-PAHs in polluted air on intrauterine
growth retardation and low birth weight. Choi et al. [17] published the results of another study from Krakow. Personal exposure of mothers
to B[a]P in the first trimester was 2.11 ng/m3 during March-May and 7.21 ng/m3 during December-February. This study showed a significant negative impact of c-PAHs
on the growth of the fetus during the first trimester. In our study, there were significantly
more newborns with a birth weight under 2,500 grams in O. south than in the other
regions of Ostrava [18]. PAH-DNA adducts have been detected in cord and maternal blood [19] and placentas [20]. Prenatal exposure to c-PAHs may be associated with altered lymphocyte immunophenotypic
distribution in cord blood [21] and changes in cord serum immunoglobulin E levels [22]. When exposed children were followed until school age, it was observed that prenatal
exposure to c-PAHs induced behavioral deficits and neuromotoric disturbances [23-26] and increased the prevalence of asthma bronchiale [27].

Biomarkers of genotoxicity in newborns were compared in a cohort of newborns in Prague
and the town of Ceske Budejovice in the southern part of the Czech Republic. B[a]P
concentrations and DNA adducts and micronuclei in the leucocytes of cord blood were
higher in Ceske Budejovice than in Prague. Moreover, logistic regression suggested
a possible association of B[a]P exposure in the third trimester with the percentages
of micronuclei in cord blood [28]. These results support the view that prenatal exposure to PAHs can induce a developmental
dysbalance of the immune system. However, in our study we have no data on personal
exposures, and the data from the monitoring station in R&B are available only since
2003 and for O. south they are completely missing.

We have confirmed the highest prevalence of wheezing during the first 5 years of life
in children born and living in the district R&B. These children also had the highest
prevalence of allergic rhinitis and of atopic eczema, which may indicate a higher
probability of developing permanent asthma bronchiale [29]. The two-stage hypothesis of Gern [30] says that environmental exposures interact with genetic factors during the prenatal
and postnatal periods to adversely influence the development of innate and adaptive
immunity, which in turn increases the risk for allergic sensitization and atopic diseases.
In the second stage, immune dysregulation in infancy increases the risk of developing
lower respiratory infections that cause airway inflammation and structural changes
during a particularly vulnerable period of lung development, leading to an increased
risk of asthma by age 7 years. This hypothesis is applicable to the effects of c-PAHs.
As far as the mechanisms of the prenatal effects of c-PAHs are concerned, it has been
found that during the fetal phases of development, c-PAHs can change the methylation
pattern of CpG cytosine in fetal DNA. Methylation of the promotor parts of genes silence
their expression. Several studies reported an association of this type of prenatal
effect of c-PAHs with the presence of wheezing in children at the age of 5 years.
The presently available data on environmental epigenetics of asthma bronchiale in
children have been reviewed [31,32]. Maternal exposure to c-PAHs during pregnancy was also associated with the methylation
of the promotor of the IFNγ gene, which may be associated with the differentiation
of naive CD4+ T lymphocytes into proallergic TH2 helper lymphocytes [33]. The results of studies on the genotoxicity of c-PAHs performed in the Ostrava region
in adults and in vitro were reviewed by Sram et al. [1].

In the WHO review [13] it is stated that there is increasing evidence for the effects of coarse particles
(PM10-2.5) on human health, independently of the effects of PM2.5. When we stratified the morbidity of O. east children in the 1st year of life according
to the year of birth, the highest incidences of URI, intestinal infectious diseases
and viral illnesses were found in children born in 2003. On the other hand, the children
born in 2004 had the lowest incidences of all illnesses except URI. The incidence
rate of URI in the first and second year of life of children born in 2003 and 2004
was significantly higher than in children born in 2001 and 2002, and it was not associated
with the season of birth. The incidence plots of URI, viral illnesses and intestinal
infectious diseases (Figure 7) resemble the 2001–2004 plots of the yearly means of PM10 in Ostrava (see the data in Table 2). From the Czech Hydrometeorological Institute data [34] it follows that this oscillation in the yearly means of PM10 was common throughout the Czech Republic and was therefore due to meteorological
factors. The time differences in morbidity were limited to children living in O. east
and support the view that ambient air pollution affects morbidity in infants.

Figure 7.The incidence (per 100 children/year) of upper respiratory infections (URI, the right
y axis), viral diseases (left y axis) and intestinal infectious diseases (left y axis) in the first year of life in infants stratified by the year of birth.

Our study is a retrospective study. The data were extracted from pediatric documentation.
The advantage of this approach is that the records were made at the time of illness
and therefore are not memory biased. The disadvantage is, on the other hand, that
the effects on morbidity of additional factors, such as children’s way of life (their
physical activity, nutrition, etc.) cannot be followed. From the published studies
(most of them concerned with schoolers) it follows that there is a connection between
life style of children and their parents, the latter of which is dependent on their
socioeconomic status e.g., [35], the proxy being mothers’ education. In a systematic review of the studies on unfavorable
health outcome related to sedentary behavior of children aged 0–4 years, only low
to moderate evidence was reported for the adiposity, psychosocial health and cognitive
development [36]. In our study, a high incidence of acute respiratory infections in O. east children
was already present in the 1st year of life when the vast majority of children were
breastfed. Later on (in the 3rd, the 4th and the 5th year) from 40 to 90% children
visited day care, which increased their risk of their being infected (Table 4).

Conclusions

In comparison with children living in the other regions of Ostrava, the children born
and living for 5 years in the region Ostrava east (most of them in the highly polluted
district R&B) had: a higher incidence of upper respiratory infections, pneumonia,
tonsillitis, intestinal infectious diseases and unspecified viral infections (ICD10
code B34). They also had the highest prevalence of wheezing (37%), atopic dermatitis
(35%), allergic rhinitis (24%) and their combinations. Among the four regions of Ostrava,
the highest yearly means of PM10 and benzo[a]pyrene (in 2006) were recorded at the monitoring station in R&B, whereas
the lowest yearly concentrations of both PM10 and benzo[a]pyrene occurred in the region Ostrava west with a low morbidity in children.
In multivariate models the effects of the region of residence on morbidity in children
were not modified by any covariate. Our data are in agreement with the literature
data which show that prenatal exposure to benzo[a]pyrene presents a considerable risk
to multiple organ systems with negative consequences for postnatal development.

Competing interests

The authors declare that they have no competing interests.

Authors’ contributions

MD collected the field data, performed the statistical analysis and drafted the manuscript.
AP supervised digitalization of the field data, constructed the final database and
took part in performing statistical analysis. VS was responsible for data on pollution
of the city of Ostrava. SR and ER calculated the yearly means of PM10 for each locality of residence using GIS and the data from surrounding monitoring
stations. ES provided advice about composition of questionnaires and analysis of ICD-10
codes. Author RJS conceived the study and participated in its coordination and in
drafting the manuscript. All authors have read and approved the final manuscript.

Acknowledgements

This work was supported by the Ministry of the Environment of the Czech Republic (Airgen
SP/1b3/8/08)and the Grant Agency of the Czech Republic (P 301 – 13458 S). The study
would not have been possible without the close cooperation of pediatricians and pediatric
nurses in the city of Ostrava. We thank to Jim Dut for critically reading the manuscript.

Jedrychowski W, Galas A, Pac A, Flak E, Camman D, Rauh V, Perera F: Prenatal ambient air exposure to polycyclic aromatic hydrocarbons and the occurrence
of respiratory symptoms over the first year of life.